Duquesne University

John F. Stolz, Ph.D.

Director, Center for Environmental Research and Education;
Professor, Environmental MicrobiologyBayer School of Natural and Environmental SciencesDepartment of Biological Sciences; Center for Environmental Research and Education

Education:

My current research centers on the physiology and biochemistry of bacteria that transform metals and metalloids as well as microbial community structure.

Microbial Arsenic Transformation

Arsenate eating bacteria can mobilize arsenic from rocks and sediments, transforming it into their more toxic forms (i.e. AsIII). As a consequence, over 30 million Bangladesh are suffering from arsenicosis due to microbial mobilization of arsenic in their drinking wells. Arsenic can be important factor in the microbial ecology of lakes and subsurface waters. In Mono Lake and Searles Lake, a robust arsenic cycle drives the microbial ecology. Our most recent discovery is that As(III) can serve as the electron donor in anoxygenic photosynthesis. Through the courtesy of the DOE Joint Genome Institute, four of our arsenic metabolizing organisms (Alkalilimnicola ehrlichii, Alkaliphilus oremlandii strain OhILAs, Bacillus selenitireducens, Deltaproteobacterium MLMS-1) have had their genomes sequenced and we are completing their annotation. The genome data has allowed us to use a proteomics approach for elucidating the pathways of inorganic and organic arsenic transformation. In collaboration with Dr. Aaron Barchowsky (School of Occupational and Public Heath, U Pitt), we are investigating the change in microbial community that occurs in the lower GI tract in response to arsenic exposure. In collaboration with Dr. Partha Basu (Department of Chemistry and Biochemistry), we are studying the microbial transformation of roxarsone, an organoarsenical fed to chickens. We also continue the collaboration with Ronald Oremland (US Geological Survey) isolating and characterizing new species of bacteria (i.e., 16S rRNA), purifying and characterizing the terminal reductases and cytochromes involved in the reductive pathway, cloning and sequencing the genes encoding them, and developing biochemical and molecular probes for their detection in the environment. This work involves bacterial physiology, molecular biology, protein biochemistry, and field work. It is currently supported by NASA, NIEHS, and the NSF.

Chromate Reduction in the Presence of High Nitrate

Many factors are involved in the remediation of specific radionuclides and metal contaminants at DOE sites. The contaminants are often mixtures with other metals and metalloids. Nitrate is commonly found at DOE sites and presents a challenge for bioremediation. Strategies for transformation of radionuclides (i.e., uranium, technetium) and metals (i.e., Cr(VI), Hg) that involve reductive processes can be inhibited by nitrate. Thus a better understanding of how nitrate metabolism directly impacts these reductive processes is necessary. The focus of this work is to determine how respiratory nitrate reduction to ammonia (RNRA) impacts Cr(VI) reduction to the less toxic Cr(III). The goal is to elucidate the specific mechanism(s) that limits Cr(VI) reduction in the presence of nitrate and to use this information to develop strategies that enhance Cr(VI) reduction (and thus detoxification) in support of the BER long term goal. We are investigating the affects of chromate on nitrate respiration in three different metal reducing bacteria, Geobacter metallireducens, Sulfurospirillum barnesii, and Desulfovibrio desulfuricans. We have discovered that each has a unique response to Cr(VI) when they are grown on nitrate, but all rapidly reduce Cr(VI) to its less toxic form Cr(III). Using a proteomic approach, we are looking at levels of protein expression of these organisms grown under different growth conditions to identify candidate proteins that may be involved in Cr(VI) reduction. We are also investigating the function of periplasmic nitrite reductase (Nrf) as a chromate reductase. The results will provide insight into possible amendments and manipulations for enhanced in situ remediation. This work involves bacterial physiology and proteomics in collaboration with Dr. Partha Basu. The work is currently funded by a grant from the DOE-ERSP.

Community Structure in Modern Marine Stromatolites

Stromatolites are the oldest living ecosystem on the planet. These laminated structures dominated the Proterozoic world. Today they are found in the warm waters of the Caribbean and South Seas. The microbes are involved in the deposition of sediment and the lithification (cementing) of these structures. We are studying the lithification process and microbe-mineral interactions in stromatolites from the Bahamas using light, confocal, and electron microscopy.